1. Field of the Invention
The present invention relates to an organic electroluminescent device. In particular, the present invention relates to the organic electroluminescent device forming a contact part contacting with a scan electrode layer on a scan-connecting electrode, and supplying electric current to an emission part through the contact part.
2. Description of the Related Art
Organic electroluminescence is a phenomenon forming an exciton by combining an electron and a hole supplied through the cathode and the anode, respectively, in an organic layer, and emitting light with specific wavelength by energy of the exciton.
FIG. 1 is a top view showing the organic electroluminescent device using the organic electroluminescence. FIG. 2 is a sectional view taken along the line of II-II of FIG. 1.
The organic electroluminescent device has a general structure as shown in FIG. 2. The organic electroluminescent device comprises a transparent substrate 1, an ITO transparent electrode 2 for the anode, patterned in one direction on the transparent substrate 1, an insulation layer 3 deposited on the remaining area except an emission part 20 of the organic electroluminescent device, a wall 4 formed in the crossing direction to the extended direction of the transparent electrode 2 on the insulation layer 3, an organic layer 5, and a metal scan electrode layer 6 for the cathode.
FIG. 3 is a sectional view taken along the line of III-III of FIG. 1. The scan electrode layer 6 placed between the walls 4 along the line of III-III of FIG. 1 is defined as a scan line.
An ITO connecting electrode 10 is provided to supply the current to the scan electrode layer 6 of the organic electroluminescent device as shown in FIG. 3. ITO is a metal made by doping tin oxide (SnO2) to indium oxide (In2S3), and so has satisfactory transparent property, but has a problem of high electric resistance.
Therefore, a method to supply the current to the scan electrode layer 6 fluently, as shown in FIG. 3, is one to form a scan-connecting electrode 11 made of a lower electric resistance material than ITO on the connecting electrode 10.
The organic electroluminescent device gradually requires supply of increased current in order to increase the emission area and to achieve the display with high brightness. However, the contact resistance by contact of the different kinds of materials is generated between the scan-connecting electrode 11 and the scan electrode layer 6. Thus, if the contacting area is not more than a certain size, that is, unless the contact resistance is less than a certain value, the brightness is decreased because the current cannot be sufficiently supplied into the organic electroluminescent device.
In this case, desired brightness cannot be obtained even though the applied voltage is sufficiently increased. Another problem therein is that the organic electroluminescent device is deteriorated by heat generated from the contact resistance by the increased amount of current.
This can be explained by Ohm's law (I=V/R), wherein V means voltage, I means current, and R means resistance. Here, the voltage (V) should be increased in order to increase the current (I) for high brightness. However, if the contact resistance (R) generated between the scan-connecting electrode 11 and the scan electrode layer 6 is increased, the effect of the increased voltage (V) is offset.
Also, the increase of resistance (R) causes a problem to increase heat (Q) generated therefrom because the heat (Q) per hour generated by resistance (R) is defined as Q=I2×R.